In embedded integrated circuit applications, such as automotive applications, embedded devices include display controllers for, say, infotainment, instrument cluster displays, etc. In order to enable dynamic content creation, with minimal central processing unit (CPU) intervention, it is known for such embedded display controllers to read (e.g. fetch) image data for individual graphics layers so that they can be displayed directly from memory and thereby blended on-the-fly to generate one output image.
Graphical images displayed by automotive infotainment and instrument cluster displays are typically made up of a plurality of graphic layers that are combined (often referred to as ‘blended’) together in order to generate a composite image that is displayed to an end user. Accordingly, the embedded display controllers mentioned above fetch pixel data for multiple graphics layers, blend the pixel data for the multiple graphics layers to generate pixel data for the composite image to be displayed, and output the generated composite pixel data to a display device, all ‘on-the-fly’.
Such embedded display controllers are typically implemented as hardware, and include a memory interface component that supports a plurality of data channels, each data channel arranged to receive pixel data relating to one graphics layer and store the received pixel data within a respective input (First-In-First-Out) buffer. The display controller may then perform functions, such as format conversion, blending, gamma correction, etc., ‘on-the-fly’ in order to generate composite pixel data to be output to a display device. Blending is performed to combine multiple graphical surfaces, e.g. blend multiple picture/pixel rectangles, in order to form a single image for a display. It is known that this function can be off-loaded from or to other processors that are normally responsible for it (such as the central processing unit (CPU) or graphical processing unit (GPU)).
A problem encountered by such display controllers is that the number of graphical surfaces/number of picture or pixel rectangles that they are capable of blending simultaneously is limited. If this blending limit is exceeded, the visual result will be incorrect. Conventionally, any graphical surfaces (e.g. number of picture or pixel rectangles) beyond the display controller blending limit are thereafter ignored by the display controller, with the respective pixel data being left out of the composite pixel data that is displayed. For example, if we assume that a display controller is able to only blend a maximum number of six surfaces simultaneously, then if it is requested or required to blend seven surfaces, then one surface will be completely ignored and the entire output will be incorrect, as it will have ignored the contribution of one surface. In optimized display systems, the graphics layers are dynamically assigned in order to ensure the highest priority graphics layers are blended within the composite pixel data. However, any additional graphical surfaces or number of picture or pixel rectangles beyond the display controller blending limit will still not be included within the composite pixel data, and their information will be ‘lost’ from the displayed image.
A number of solutions have been attempted to address the problem of detecting pairs of overlapping pixel rectangles, such that they can be blended, such as U.S. Pat. No. 7,505,048B2, U.S. Pat. No. 6,917,877B2, US20140258253A1 and U.S. Pat. No. 5,831,628A. However, the computational cost of using these solutions of detecting pairs of overlapping rectangles in order to obtain all of the maximal (largest size) sets of simultaneously-overlapping rectangles is impractical, as will be shown later. The maximal sets themselves are required so as to determine when a group of layers cannot be blended simultaneously by a display controller. A less complex solution is therefore needed.